The present invention relates to a control device of a sewing machine feeding system, which is installed with independently controllable feeding elements so as to sew a workpiece in a stretched, neutral or compressed condition.
On an international exhibition for shoe production (IMS 1979, Pirmasens/Germany) a sewing machine installed with a differential feeding system with a control device was presented, which may be applied for performing ruffling sewing operations at which the ruffled fullness or surplus of material was fixed by a seam or by a fixing tape. In order to simplify this operation, the sewing machine was installed with a control device, in which various rates of fullness may be stored and which may be referred to by a number of push buttons. Besides a number of push buttons, the control device was installed with a selector switch that allowed the operator to put in a further value of feeding movement which is not available in the control device such as a neutral feeding rate, i.e. the workpiece will be fed by the feeding elements at equal feed rates. By actuation of an additional switch, the operator is enabled to either select the feed rates set in the control device, or the feed rate put in by the selector switch during the sewing operation.
At the exhibited sewing machine the adjustment of the stitch regulating mechanism cooperating with the feeding elements engaging the workpiece was performed by a cam disc installed on a shaft of a gear motor. By the selection of various feed rates the cam disc was positioned in various angular positions by the gear motor connected to the control box in a closed loop arrangement.
In U.S. Pat. No. 3,855,956 there is shown a mechanism for converting digital information in a control movement of a regulating element. Such a mechanism having jointly connected levers of different lengths selectably displaced by solenoids and generally considered as a digital linear motor, is suited to quickly alter the shifted conditions. However, this mechanism allows only to execute short distances of travel at relatively low forces.
Accordingly, it is a main object of the present invention to provide a simple control motor which does not require a closed loop controlled gear motor.
It is a further object of the present invention to install the differential feed sewing machine with a low-cost adjustment device, which is simple in design and reliable in operation.
Still another object of the present invention is to provide an adjustment device of space saving design and which also allows handling of higher adjustment forces.